TDS=Total Disolved Solids, PPM and EC are all pretty much about the same thing just depending on where you are is which one is used more. Just like some peeps have a Roof over their heads while others have a Ruff overhead. Tomatoe and Tomata, Soda and Pop and for the Mass peeps car and caaaaar. Hopefully you will understand why I spelled things the way I did :thumbsup: